In commercial dyeing of fabric, typically at least when the same is formed as piece goods, the fabric is immersed in an agitated liquid bath of water and appropriate dyes and chemical additives. The actual dye cycle provides that the bath and the goods in the bath are heated from a low inactive temperature, possibly at the infeed tap water conditions of 50.degree. - 80.degree. F, to above the temperature at which the dye strikes or reacts with the fabric. Depending on the fabric and the type of dye used, some dye activity, or migration out of solution to the fabric, might exist at low temperatures near 150.degree., moderate dye activity usually takes place at higher temperatures near 180.degree. F, and all dye should be exhausted from the solution at boil . . . especially after a dwell time in excess of several minutes. After the dye strike temperature is reached and held the required dwell time, the bath is cooled and drained, and the goods are then rinsed and dried.
Potential factors for rejecting any batch of dyed goods include non-uniform coloring or shading of the goods, poor texture or feel of the goods without the desired fluffiness created by proper mild fiber abrasion during the dye cycle, stretching or bruising of the goods that might occur during a dye cycle having inadequate or excessive bath agitation, or thermal fracturing or cracking of the synthetic fibers occasioned during cool down.
One type of commercially available dye machine is a rotary dyer, having an outer shell holding the dye bath and an inner perforated tub holding the goods to be dyed and rotated through the dye bath. Another type of commercially available dye apparatus is a paddle wheel dyer, where a large tub holds the dye bath and goods, and where the rotating paddle wheel churns the bath to float goods therein. The newly introduced type of commercial available dye machine, known as the SLANT LINE, has an inclined rotatable tub that holds both the dye bath and goods, and further has a pump that circulates the bath through the goods. This latter type is disclosed in my co-pending application Ser. No. 680,231, filed May 12, 1976.
One major problem of most commercially available dye machines is the large amount of water that must be used in order to dye the many varied fabrics with repeatable commercial success. In order to compare different dye cycles, the amount of water required for each dye bath is reduced to a water to goods ratio, obtained by comparing the weight of the dye bath water to the dry weight of the goods to be dyed. In considering the water to goods ratio, the weight of water required to wet out the goods is not considered, nor is the weight of water used to heat and cool the bath. The apparatus for and method of dyeing goods disclosed in my co-pending application Ser. No. 680,231, filed May 12, 1976, operates with a water to goods ratio as low as 2 to 1 and consistently in the range below 7 to 1. This low level dyeing is compared to the water to goods ratios in excess of 10 to 1 and even as high as 20 to 1 more commonly experienced in the rotary and paddle wheel dyers.
In the face of ever increasing costs, low level dyeing represents a significant advancement to the dyeing art, considering only for example the reduced energy costs required to heat the smaller bath to the boil and the reduced chemical costs where specific chemical concentrations are required in the smaller bath. However, the area that yet remains very critical in this low level dyeing apparatus and method is the cool down of the goods from the dye strike temperature at or near the boil through the sensitive range above approximately 156.degree. F where the fabric may yet be thermally unstable.
In this regard specifically, orlon is the most commonly used fabric for men's socks for example, and yet is most critical as to how it must be dyed. Orlon itself is thermoplastic at temperatures in excess of approximately 156.degree. F, so that fiber cracking or fracture can occur upon exposure to too rapidly changing bath temperatures above this. Balling up or knotting of the goods during cool down is particularly problemsome since this only randomly exposes the goods to the bath and almost always results in thermal cracking. Bath agitation frequently can be used to maintain the goods open and thus less subject to thermal cracking, but inadequate or excessive agitation can bruise the fibers and thus by itself is not the solution.
The apparatus disclosed in my co-pending application Ser. No. 680,231 acceptably controls the cool down rate by regulated infeed of cooling water and prompt mixing of this water with the bath exteriorly of the tub, while the pump circulation of the bath through the tub and the agitation of the bath in the rotating tub provide uniform exposure of the goods to the bath. However, even in the face of elaborate and sophisticated controls, the available tolerance of variables is extremely limited.